Patent GB-521623-A (GB)
Title: Pressure control system for use in connection with aircraft pressure-cabins
IPC: B64D13/02
Filed: 1938-11-23
Abstract: 521,623. Aircraft cabins. CLEVELAND, F. J. (Boeing Aircraft Co.). Nov. 23, 1938, No. 34092. [Class 135] The invention relates to means for supplying air to a pressure-cabin of an aircraft and for controlling the pressure therein, and is distinguished mainly' by the use of pressure-sensitive devices for maintaining a chosen constant pressure in the cabin within a certain range of external pressures (e.g. up to a given altitude), and other pressure-sensitive devices for maintaining a chosen difference of internal and external pressure within another range of external pressures (e.g. above the given altitude), whereby excessive stresses on the cabin structrue are avoided at high altitudes. In one form, Fig. 1, air is supplied to a cabin by a supercharger 9 through an inflow conduit 90, a control device M, a branched conduit 92. and outlets 93. The air passes through a steam heater 91 controlled by a thermostat 83 and supplied by a boiler 81 heated by the engine exhaust pipe 80. The air is discharged from the cabin through inlets 94 and outlet conduits 95, 96, the former passing through the control device M. Air may also be supplied to the cabin by a scoop through a conduit 97 and discharged through inlets 99 and a conduit 98. Passenger-controlled ventilators may be supplied from one or both of the conduits 92, 97, e.g. by a branch pipe 97<SP>1</SP>. At low altitudes, e.g., 0-8,000 feet, the cabin is sumpplied through the conduit 97 but, at a given altitude, an alarm signal is given by a pressuresensitive device Y and valves 7, 70 controlling the conduits 97, 98 are closed by solenoids 71, 72 operated manually or by the device Y which may be adapted to set the supercharging system into operation automatically. A further alarm may be provided or the device Y used in another circuit to give a signal when the limit of the capacity of the supercharging is reached. The control device M, Fig. 2, comprises a valve 1 controlling flow between the conduits 90 and 92 and a valve 2 controlling flow between the conduits 95 and' 96. The valves are controlled respectively by a piston 11 carrying a stem 18 acted on by a spring 100, and by a spring-loaded evacuated syphon 21 acted on by the cabin static pressure and carrying a stem 27. The valve 1 may be used manually by a handle 19. The movements of the valves 1 and 2 are assisted by pistons 13 and 24. The spaces above and below the piston 13 are in communication with the atmosphere through a pipe 15 and check valve 16 and a pipe 14 respectively and the upper space may also communicate with the conduit 90 through a passage in the stem 17 of the valve 1 which is controlled by the stem 18. The space below the piston 24 communicates with the conduit 90 through a passage 25 while the space above the piston may communicate with the conduit 96 through a passage in the stem 22 of the valve 2 which is controlled by the stem 27. The space above the piston is also connected by a pipe 26 and a valve 42 with the atmosphere, the valve being controlled by a spring loaded bellows 4 the interior and exterior of which are under the influence of atmospheric pressure and cabin pressure respectively. Counter weights are provided on the valves to eliminate inertia effects due to the motion of the aircraft. A control valve 3 is provided which is operated manually or automatically through a handle 30 and has passages 31, 32 terminating in four ports which register with four of six pipes 33, 34, 35, 36, 37 and 38 in each operative position. The positions shown in Figs. 3 and 2 are those assumed when air is supplied to the cabin through the conduit 97, and when the supercharging system is operating. In the position shown in Fig. 3, the space below the piston 11 is connected with the throat of a venturi 10 provided in the conduit 92 by the valve passage 31 and pipes 33, 34, while the space above the piston is connected through the pipe 36, valve passage 32 and pipe 37 with the conduit 92 on the pressure side of the venturi. The rate of flow of air into the cabin due to the supercharger is thus kept substantially constant since any variation in flow will alter the pressure difference in the spaces above and below the piston 11. If, for example, the flow increases, the piston 11 moves downwardly against the spring 100 and opens the passage in the stem 17 thus admitting supercharger pressure to the space above the piston 13 and closing the valve 1. The sylphon is arranged to be collapsed by the cabin pressure while air is supplied by the conduit 97 so that the valve 2 is kept open. At a given altitude, a pressuresensitive device 5, Fig. 5, of the device Y is operated to close contacts 51 and light a lamp 54. A switch 52 is then moved manually or automatically to engage a contact 53 ; this energizes solenoids 71, 72 to close the valves 7 and 70 and move a member 39 connected to the handle 30 to move the valve 3 to the position of Fig. 2. In this position of the valve the space above the piston 11 is in communication with the cabin pressure through the pipe 35, valve passage 32 and pipe 36, and the space below the piston is connected to venturi 20 provided in the conduit 95 by the pipe 33, valve passage 31 and pipe 38. At the given altitude, due to the decreased cabin pressure, the sylphon 21 commences to expand and close the valve 2. The sylphon is arranged to expand completely in response to a given small variation in cabin pressure. Any variation in cabin pressure will therefore alter the position of the valve 2 and consequent variation in the rate' of flow from the cabin will influence the valve 1. The cabin pressure is thus maintained substantially constant. At a higher altitude, when the difference between the atmosphere pressure and the cabin pressure reaches a given amount, the bellows 4 is operated and puts the space above the piston 24 in communication with the atmosphere. For higher altitudes the valve 2 is therefore controlled so that a constant difference exists between the cabin and atmospheric pressures. When the limit of the capacity of the supercharger is reached, a pressure-sensitive element 50, Fig. 5, is operated to close contacts 56 and again light the lamp 54. The valves 1 and 2 also act to prevent loss of air should the supercharger fail and to prevent atmospheric pressure exceeding cabin pressure. The valve 3 may be modified so that the valve 1 is under the influence of inflow and outflow conditions at the same time. The sylphon 21 may be replaced by a flexible container containing a volatile liquid, and the venturis, by hot wire flow meters, so that pressure and flow control is also in accordance with atmospheric or cabin temperature. In another form, Fig. 7, air from the supercharger enters the cabin through a conduit 9<SP>1</SP>, past a valve 190 having a hollow stem 191, and through a venturi 193, and leaves through a venturi 183. past a valve 180 having a hollow stem 181, and through a conduit 8'. The valve 190 is controlled by' a piston 197 carrying a stem 197' and influenced by a spring 198<SP>1</SP>, the spaces above and below the piston being in communication respectively with cabin pressure through a pipe 196 and with the pressure at the throat of the venturi 183 or 193, or the pressures at both, through pipes 183<SP>1</SP>, 193<SP>1</SP> and 199. A valve such as 3, Fig. 3, may be provided to control the pipes 183' and 193<SP>1</SP>. Movement of the valve is assisted by a piston 194, the space beneath which is in communication with the cabin pressure through a pipe 195' and the space above with supercharger pressures through a passage in the stem 191 controlled by the stem 197<SP>1</SP>. The valve 180 is connected to a piston 184, the space beneath which is in communication with cabin pressure and. the space above which may be in communication with atmospheric pressure through the passage in the stem 181 or through pipes 173, 174. The passage in the stem 181 is controlled by a pin 187 connected to a lever 188 fulcrumed at 186 and acted on by a spring 189. The other end of the lever is connected to a piston 7' having a port 171 controlled by a pin 172 connected to a spring-loaded bellows 175 exposed to cabin pressure. The pin 187 is also controlled by a spring-loaded piston 6' adapted to engage a shoulder 187' on the pin, the spaces above and below the piston being in communication with atmospheric and cabin pressure respectively. A device shown'in Fig. 10 is interposed between the pipes 173. 174 and comprises a chamber 1, arranged inside the cabin, having a bleed port 110 and a flexible wall 111 connected by a rod 131 with a sleeve 3' slidable in a sleeve 4<SP>1</SP> in turn slidable in a sleeve 2'. The pipe 174 is connected to the sleeve 4<SP>1</SP> and the pipe 173 to the sleeve 2<SP>1</SP>, communication between the pipes being through a groove 124, port 142 and groove 144. An atmospheric line 178 is connected to the sleeve 2<SP>1</SP> adjacent a groove 123, and the sleeve 4' is also provided with a groove 143 and port 141. Locks 130 and 120 are provided for the rod 131 and sleeve 2' and are operated by a knob k, Fig. 8 (not shown) which latter also operates suitable' cams to shift the sleeves 2<SP>1</SP>, 4<SP>1</SP> in relation to each other and to the sleeve 3<SP>1</SP>. The operation of the apparatus is as follows. Below a given altitude, with the device of Fig. 10 inoperttive, the bellows 175 is completely collapsed and the reduced pressure above the piston 184 balances the downward force exerted on the valve by the outflow. The valve is therefore maintained open by the cabin pressure acting beneath the piston. The inflow is kept substantially constant by the valve 190. At given altitude the bellow expands and restricts the port 171. The balance between the pressure above the piston 184 and the downward force of the outflow is thus destroyed and the valve 180 closes against the cabin pressure beneath the piston. The pres